Update 8 Aug 2011

Same phone a few months later … now I can’t hear music play even with headphones / earbuds.
+ when someone phones me the ringer doesn’t sound
BUT when I answer the phone with headphones on then I can hear them!
(although apparently they can’t hear me)

So, as before, I pushed the headphone jack in & out several times, but the problems remained.

Then, following instructions in the link above, I put a bit of lubricant (GT85) in the socket that takes the headphone jack

Then I pushed a couple of different jacks in & out of the socket a number of times and eventually … I could now hear sound through the headphones, but still couldn’t hear anything without the headphones.

Then after a bit more lubricant, and inserting and removing the headphones again, sound returned to normal. Phew!